The dome has a square on top and 4 square around the bottom that are convenient for placement of doors, windows, and extensions.
Height: 13 ft 9 inches [65% of diameter]
Ground perimeter has 12 edges, and is 20 ft across, 95% of diameter.
Door shown is wide and short - 45" x 75". Longest struts in this case are ~75" so the dome could easily be larger, using 8 ft lumber, and fit a standard size door in the square area. In fact if 8 ft struts are used, dome diameter becomes 27 ft-6 inches and height is almost 18 ft. Square areas become approximately 8 ft. x 8 ft.
With the -X1 subdivision, all triangles are halved into right triangles. Four rectangle zones are created in lower areas that can be used for a wider door/extension. On the 21 ft dome this size is 107 x 75 inches. The hemisphere line can now be seen in the mid-level row of 16 struts. This shows where a vertical riser (or VBO) might be used in place of geodesic hubs and struts, or cut off point for a half dome of either -X1 or non -X1 dome.
Similarities with the RCO-S [Simplified Rhombi-Cubocta Dome] can be seen. This Octa Dome 4 Cl. 2 dome has more varieties of struts and hubs and more roundness. Like the RCO dome, the top 1/3 can be made flat = level and placed on a conventionally built riser wall.
The Hexagon Zenith is made by turning the dome 90° resulting in a 6-way Connector Hub at the apex-zenith.
Additional illustrations of the Octa Dome 4 Class 2 HZ